Spare tire
 

Does anyone know if it is safe to use a Spare tire from an S40 size 16 on my S70 size 15 it fist and drive,but I hear from 1 source that it is not safe,and that it can Hurt my transmission,is that true?

With AWD transmissions you don't want to use tires of different diameters or you can kill the center diff.

My S70 is not AWD

So anyway, what matters about tires is the outer diameter of the tread, not the rim. If your car is front wheel drive, then the sizes of the two rear tires can be different and it would mechanically have no effect at all. Handling would be affected, and in fact it's affected with the correct size spare. Braking, play close attention and decide yourself it you think it's okay. If they are very different, the ABS will see different speeds and that might cause it to turn a light on or not work exactly right.

Thanks Firebird.
This is what I suspected but wasn,t completely sure.